Fresh cut and segmented fruit pieces have traditionally been marketed for further processing or manufacturing (e.g., pie filling or canning). It has more recently become popular for restaurants, fast-food establishments and institutions such as hospitals, prisons and the army to purchase fresh chilled "ready-to-use" fruit and vegetables to reduce labor costs and facilitate portion control in their operations. Some supermarkets are now providing salad bars where customers can prepare their own salads from freshly cut fruit and vegetables. However, fruit salad ingredients such as fresh cut and segmented apple, pear, nashi and banana pieces will show physical signs of deterioration, particularly enzymatic browning and microbial spoilage in a fairly short period of time (i.e. 1-3 days). Retail marketing of prepacked cut and segmented fresh fruit pieces could increase in the future provided the shelf life of this fruit can be extended beyond 7 days. An opportunity also exists in exporting fresh chilled fruit pieces if the shelf life could be at least 7 days under chilled or refrigerated conditions (1-6.degree. C.).
As browning is an oxidative reaction it can be retarded by the elimination or reduction of oxygen from the cut surface of the fruit. However, browning will still occur when oxygen is reintroduced. Most of the currently available methods or compositions for inhibiting discolouration in fresh cut fruit pieces are used in conjunction with vacuum packaging, gas packaging or other similar techniques. AU 607200 describes a process based on gas packaging fresh fruit pieces in a high gas barrier container with a gas mixture containing carbon dioxide, oxygen and other inert gases such as helium, argon and hydrogen. This process has various limitations including reliance on package integrity, fermentation of the product under temperature abuse conditions and the high costs of gas packaging equipment and packaging materials.
Reduction of oxygen is possible by treating fresh uncut fruit with surfactants as described in EP 0275710. This process has limited application to fresh cut fruit pieces because the oxygen barrier may only be temporary. The use of surfactants in fresh cut fruits are not permitted by food regulatory bodies in most countries.
A more popular approach for the prevention of browning in fresh cut and segmented fruit and vegetables has been the use of antibrowning agents. Antibrowning agents are compounds that either act primarily on enzymes or the substrates and/or products of enzymatic catalysis in a manner which inhibits pigment formation. Antibrowning agents which have been previously disclosed for use in preventing color deterioration include ascorbic and other edible acids, sodium phosphates, sodium ascorbate, potassium ascorbate and sulphites.
The most widespread methodology used to control browning in fresh cut fruit and vegetables is the addition of sulphites. Although sulphites are very effective in the inhibition of enzymatic browning reactions, there are several negative attributes associated with their use in food. Sulphites are known to cause adverse health effects, especially in certain sensitive individuals such as asthmatics. Sulphites can also give negative effects on the taste of food. In the United States of America, the Food and Drug Administration (FDA) has banned sulphites for use in fresh salad bars. The use of sulphites in Australia is currently permitted only on fresh cut and segmented fruit pieces intended for manufacturing or further processing. However, more manufacturers and processors are now giving preference to fresh fruit pieces that have not been treated with sulphites.
Treatment compositions especially those containing sulphites are often used in conjunction with vacuum packaging using impermeable or high gas barrier packaging materials. Vacuum packaging generally creates anaerobic conditions which are conducive to anaerobic fermentation which can produce off flavors and promote the growth of pathogenic organisms. A preservative method or composition for extending the shelf life of fresh cut fruit pieces which does not rely on vacuum packaging would be of significant benefit to the fresh fruit industry.
The presence of oxygen in a package or container of cut and segmented fruit pieces is essential to reduce the risk of anaerobic food pathogen growth and avoids fermentation of the fruit pieces due to the lack of oxygen supply. Fresh cut and segmented fruit pieces are biologically and physiologically active in that their tissues are living and respiring. Fresh cut fruit pieces require oxygen to continue their normal respiratory activity. The conventional approach to allowing respiration but retard browning is to either encapsulate or coat the cut fruits or treat the cut surfaces with a solution containing anti browning agents, usually food acids.
U.S. Pat. No. 3,754,938 describes the use of an ascorbic acid-based composition containing 0.5 to 1% ascorbic acid, 0.05 to 0.1% calcium chloride and bicarbonate thereby maintaining a pH between 7 and 9 for the preservation of apple slices. U.S. Pat. No. 4,818,549 also discloses the use of an ascorbic acid, citric acid and calcium chloride composition. These compositions have limited effectiveness, as the concentration of antibrowning agents which remains on the entire surface of the fruit pieces is not sufficient.
U.S. Pat. No. 4,975,293 discloses the use of cyclodextrins and cyclic oligosaccharides as inhibitors of enzymatic browning for raw fruit and vegetable juices. Compositions containing cyclodextrins in combination with known antibrowning agents such as anti-oxidants and chelating agents are also described in U.S. Pat. No. 4,975,293. The use of such compositions has limited applications because cyclodextrins are not food approved.
WO) 91/02230 describes a technique of immersing fresh cut fruit and vegetables in an aqueous solution containing anions such as phosphate, pyrophosphate sulfate or chloride. The treated produce is then rinsed to remove the aqueous solution which could give a bitter undesirable taste. Fruit treated in this manner generally requires vacuum packaging because the effectiveness of the solution is limited to a short period of time.
The aforementioned preservative compositions which are in the form of aqueous solutions are also generally limited in effectiveness because of their inability to adhere on the sensitive cut surfaces of the fruit pieces. In order to overcome this limitation, EP 366,245 discloses a composition containing ascorbic acid and a thixotropic gum such as xantham, guar or tragacath for use in reducing the browning of fruit used in salad bars and prepared salads sold in fast food restaurants. However, this composition suffers from the disadvantages of having a slippery or slimy texture and limited adherence on the cut surfaces because the composition is an aqueous solution of high viscosity. It may be acceptable for salads which are covered in fruit juice but not for cut fruit intended to be eaten with the fingers rather than a spoon.
U.S. Pat. No. 4,504,504 discloses a sodium alginate coating which is firmed with a solution containing calcium chloride and preferably citric acid to be used on cut fruit and vegetables [particularly tomatoes] to inhibit loss of their flavor and texture during cooking.
U.S. Pat. No. 4837037 suggests treating coleslaw salad with a mixture of alginic acid and acetic acid to inhibit micro-organism growth and extend the shelf life of the coleslaw. This patent also suggests adding calcium ions to form an encapsulating coating.
A requirement accordingly exists for a preservation method and/or composition which does not contain sulphites nor use vacuum packaging, but which can be used to extend the shelf life of fresh fruit pieces by preventing enzymatic browning and microbial spoilage. It would also be advantageous for the fruit pieces to be packaged in an environment containing some oxygen so that the normal respiratory activity of the fruit tissue can be maintained.